The present invention relates to a method of winding a coil of superconducting wire for a superconducting magnet, and, more particularly, to a winding arrangement wherein the windings of the coil are uniform and dense, such that the resulting superconducting magnet produces a strong and homogeneous magnetic field and yet is physically compact and energy efficient.
Superconducting magnets and the methods of their manufacture are well known in the art. At cryogenic temperatures, superconducting wire loses virtually all ohmic resistance and allows the free flow of electricity for long periods of time and in very high current densities. Because the current density in a superconducting coil can be hundreds of times higher than in nonsuperconducting coils, very strong magnetic fields can be obtained, and, as a result, superconducting magnets have found extensive application in devices such as high energy particle accelerators, plasma confining tokamaks, synchrotron radiation sources, nuclear magnetic resonance imaging systems, and magnetic levitation devices. However, due to continuous demands for greater power and accuracy of these devices, there is a continual need for a more efficient superconducting magnet which can provide stronger and more homogeneous magnetic fields and at the same time is physically more compact and requires less power.
A prime example of the application of more efficient superconducting magnets is in the construction of the Superconducting Super Collider (SSC) particle accelerator which will use thousands of superconducting magnets to bend and focus high energy particle beams in a generally circular orbit. Although the main superconducting magnetic coils of the SSC are designed to exhibit minimal magnetic field harmonics, due to superconductor magnetization effects, iron saturation and coil positioning errors, certain harmonic errors are possible which must be corrected with multipole corrector or adjustment coils. Additionally, multipole corrector coils are utilized to focus the particle beam into a desired stream, so as the energy of the particles increases, the strength of the corrector coils must likewise be increased. Therefore, there is a need for corrector coils which can provide strong and homogeneous magnetic field and, yet, are compact and energy efficient.
Although the use of corrector coils to correct magnetic field deviations and to focus the particle beam is well known, the production and use of these coils are complicated by a number of factors. First of all, the superconducting wires utilized in the windings are typically of very small diameter and are generally more brittle than normal conductors, so therefore greater care must be exercised in the winding and forming of such superconducting magnets. Another factor is that the coils are very lengthy (more than a meter in length) while the spacing between the adjacent turns of the coil must be precisely maintained, so it is difficult and time consuming to wind uniform layers of wire which are physically stable so as to prevent generation of frictional heat from coil movement resulting from the electromotive forces of the large currents. Additionally, the coils must be physically compact so that it may easily be cooled to cryogenic temperatures.
Until now, such correction coils have been randomly wound around a mandrel to obtain the coils of desired length and then shaped into desired configurations to fit around the bore tube. However, because the windings of these previous coils were not essentially uniform, the magnetic fields they generated were neither as homogeneous or as strong as desired.
As can be seen from the foregoing, one of the requirements for an efficient superconducting magnet is that it have a uniform, homogeneous cross-section with a high density of superconducting wire within its cross-sectional area. As the windings are made more uniform and with greater cross-sectional density, the magnetic field produced by the windings is stronger and more homogeneous. This also means that the resulting superconducting magnet requires less energy and, yet, is physically more compact. These advantages would also facilitate greater flexibility in the positioning of these corrector coils about the bore tube and make it easier to cryogenically cool the same.
In nuclear magnetic resonance (NMR) imaging, homogeneous magnetic fields are required to obtain optimum image data. Although the main magnetic coil of a NMR imaging system is designed to produce a homogeneous a magnetic field as is possible, some spatial deformity is inevitable, and it is standard practice to utilize corrector coils to perturb the magnetic flux pattern to increase the overall homogeneity of the magnetic field. However, the process of measuring the magnetic field deformity and calculating the positioning and magnitude of the corrector coil current is a tedious and time consuming process. Therefore, a corrector coil that produces a more homogeneous magnetic field would simplify and speed-up the correcting process.
Likewise, in constructing synchrotron radiation and magnetic levitation devices, it is essential to have compact and efficient superconducting magnets which can produce strong yet homogeneous magnetic fields.
In view of the foregoing, the general object of this invention is to provide a method of winding a coil of superconducting wire for a superconducting magnet having a relatively dense and uniformly spaced windings to enhance the homogeneity and strength of the magnetic field produced by the superconducting magnet.
Another object of this invention to provide a mandrel for winding a coil of superconducting wire for a superconducting magnet having a relatively dense and uniformly spaced windings.
Yet another object of this invention is to provide a coil of superconducting wire having relatively dense and uniformly spaced windings.
Additional objects, advantages and novel features of the invention will become apparent to those skilled in the art upon examination of the following and by practice of the invention.